To provide a theft-prevention device fixedly attached on goods easy to be stolen, and constructed to be operated in cooperation with a releasing device.

The device includes a first member 2 including a base member 4, a connection member 6 contriving that it projects from the base member 4 and is inserted through goods, and a fixing member 8 contriving that it is attached to and fixed on the connection member 6 and fixes a theft-prevention device on the goods by preventing the movement for the direction separated from the base member. The fixing member is released from the connection member by changing the shape of a releasing member 66 comprising material having memory property provided there by temperature change.